Synergistic compositions for corrosion and scale control

ABSTRACT

Dimethylaminomethylenebis(phosphonic acid) is prepared by reacting dimethylformamide with phosphorous trichloride and treating the reaction mixture with alcohols or glycols and water. The phosphonic acid is combined with water soluble carboxylic acid polymers for use as a corrosion and scale inhibitor in aqueous systems. These compositions may also be combined with phosphorous acid and water soluble zinc salts.

This invention relates to compositions, methods of preparing thecompositions, and methods of using the compositions for inhibiting thecorrosion of metal parts in contact with aqueous systems, for inhibitingthe deposition of scale and sludge on the heat transfer surfaces ofcooling water systems and boilers, said compositions comprisingdimethylaminomethylenebis(phosphonic acid) or water soluble saltsthereof, a water soluble polymer having a linear hydrocarbon structureand containing in a side chain carboxylic acid groups or carboxylic acidsalt groups with a molecular weight of between 200 and 100,000 with oneor more of the following:

A. Water

B. An aqueous solution of phosphorous acid or alkali metal salts thereof

C. An aqueous solution of water soluble zinc salts

It is well known that the operation of commercial and industrial coolingsystems is adversely affected by a number of different factors. Of theseadverse factors, corrosion of metallic parts coming into contact withthe water is probably one of the most serious. If not controlled,corrosion causes the rapid deterioration of the metallic materials ofconstruction used in cooling towers and associated equipment such aspumps, pipelines and valves, causing major losses in overall efficiencyof the cooling systems. While control of bleedoff, pH, and otheroperating variables is helpful in reducing corrosion, chemical treatmentof the water is generally the most effective and economical means ofminimizing this problem, particularly where conservation of water bymeans of recycling is necessary or desired.

Cooling water systems are also subject to formation of scale deposits.Scaling can occur when the concentration of a dissolved substance in acooling water becomes greater than its solubility in the water. It canespecially be a problem with a substance that has an inverse solubilitycurve, that is, a material whose solubility goes down as the temperaturegoes up. Since water temperatures at or near heat-transfer surfaces aregreater than temperatures in the bulk of the system, the solubility ofsuch materials is less in these regions. Consequently, they tend toprecipitate and form scales that reduce heat-transfer efficiency.

One principal scale-forming material encountered in cooling watersystems is calcium carbonate formed by the decomposition of calciumbicarbonate. This compound not only has an inverse solubility curve, butits solubility is much lower in most typical cooling waters than almostall other potential scale-formers that might be present in these waters.Of course, calcium carbonate is soluble in acidic solutions, and as thepH of a cooling water is lowered, scale generally becomes less of aproblem. However, most cooling waters are kept on the alkaline side toreduce corrosion, and thus calcium carbonate scaling remains as apotential problem. Calcium sulfate, calcium phosphate, barium sulfate,and ferric hydroxide can also cause scale. Thus, to be a broadly usefulcomposition, a scale control product must be capable of controllingdifferent scale types.

Waterside problems encountered in boilers and steam systems include theformation of scale and other deposits, corrosion, and foam. Scale andother deposits on heat-transfer surfaces can cause loss in the thermalefficiency of the boiler and can make the temperature of the boilermetal increase. Under scaling conditions, temperatures may go highenough to lead to failure of the metal due to overheating. Corrosion inboilers and steam systems also causes failure of boiler metal and damageto steam and condensate lines.

The principal source of deposits in boilers is dissolved mineral matterin the boiler feedwater. The term "scale" is generally used for depositsthat adhere to boiler surfaces exposed to the water, while nonadherentdeposits are called "sludge" or "mud." Scale causes more difficultybecause the sludge can be purged from the system with the blowdown orcan be easily washed out, but scale can normally only be removed bymechanical or chemical cleaning of the boiler.

In natural, untreated water the main sources of scale and sludge arecalcium carbonate, calcium sulfate, magnesium hydroxide, and silica. Themost common type of scale in boilers is probably calcium carbonate, butthe most troublesome is usually calcium sulfate. The latter causes moredifficulties because its solubility decreases more rapidly withincreasing temperatures than does that of other substances, and thescale it forms is hard, dense, and difficult to remove. On the otherhand, calcium carbonate tends to form sludge more than scale, and thecalcium carbonate scales that do form are generally softer and easier toremove. Magnesium hydroxide precipitates are not very adherent and tendto form sludges rather than scales.

It is an object of this invention to provide a stable liquid corrosioninhibiting and deposit control product. More specifically, it is anobject to prepare a synergistic composition containing a bisphosphonicacid and a polycarboxylic acid which performs for scale control in thethreshold range far better than would be expected from the performanceof either class of compound alone. It is a further objective of thisinvention to provide a process for corrosion inhibition and depositcontrol in cooling water systems.

Further objectives will be evident to those skilled in the art.

All of the compositions of this invention containdimethylaminomethylenebis(phosphonic acid) or water soluble saltsthereof. This compound has the following structure: ##STR1## The twophosphonic acid groups on the molecule provide acid hydrogens which canbe converted to alkali metal, alkaline earth metal and ammonium salts.

The water soluble polymer also contained in all of the compositions is alinear hydrocarbon structure with side chain carboxylic acid groups andis exemplified by the following structure: ##STR2## where R is hydrogenor --COOH and R' is hydrogen or methyl. These polymers may be obtainedfrom acrylic acid or methacrylic acid. Polymers of maleic anhydride canbe prepared and the anhydride group hydrolyzed with water to providecarboxylic acid groups. Acrylonitrile and acrylamide polymers may alsobe hydrolyzed with hot alkaline solutions to eliminate ammonia and formcarboxylic acid salts. Copolymers of all of the monomers listed may alsobe prepared and these copolymers may be hydrolyzed to the carboxylicacid groups if the anhydride, amide, or nitrile groups are contained inthe copolymer. These polymers may be utilized as the free acid or aswater soluble salts such as the alkali metal and alkaline earth metalsalts. The polymers used in this invention are commercially available ormethods for their preparation are well known in the art.

The phosphorous acid utilized in these compositions may be anhydrous oraqueous solutions containing 50 to 75 percent of the acid.

Water soluble zinc salts which may be utilized include zinc acetate,zinc chloride, zinc nitrate, and zinc sulfate.

The preparation of dimethylaminomethylenebis(phosphonic acid) has beendescribed in U.S. Pat. No. 3,846,420, Nov. 5, 1974. Dimethylformamidewas reacted with phosphorous trichloride and then a large excess ofwater was added. Alternatively, a mixture of phosphorous acid andphosphorous trichloride is reacted with dimethylformamide. In someexamples, solvents such as carbon tetrachloride and dioxane are used inthe reaction. The yields based on the amount of phosphorous trichlorideused vary from 22 to 76 percent. The process described has a number ofdisadvantages:

1. Even when a solvent is used, the products are pasty or solid andimpossible to handle in commercial processes.

2. If a water soluble solvent is used, distillation must be used toisolate the product.

3. Hydrolysis converts every atom of chlorine in the phosphoroustrichloride to hydrochloric acid which is so irritating and so toxicthat it must also be isolated or neutralized with alkali.

4. The best yield reported is only 76 percent.

In this invention we have reacted dimethylformamide with phosphoroustrichloride and about two-thirds the stoichiometric amount of an alcoholor glycol. The reaction was completed utilizing hydrolysis with water.We were surprised that the evolution of hydrogen chloride was greatlyreduced and that alcohols and glycols could be converted in high yieldto alkyl chlorides and to dichloroalkanes. The yields ofdimethylaminomethylenebis(phosphonic acid) based on the weight ofphosphorous trichloride used were essentially quantitative in manyinstances. Although the stoichiometry is not completely understood, theoverall reaction may be characterized by the equation ##STR3##

When a solvent is required, the alkyl halide (RCl) or dichloroalkanethat is being formed may be added to the mixture when thedimethylformamide and phosphorous trichloride are reacted.

Alcohols and glycols suitable for the preparation ofdimethylaminomethylenebis(phosphonic acid) and the corresponding alkylchlorides and dichloroalkanes include, but are not limited to, methanol,ethanol, 1-propanol, 2-propanol, 1-butanol, isobutanol, sec-butanol,tert-butanol, amyl alcohols, longer chain alcohols with C₆ to C₁₈ alkylgroups, ethylene glycol, propylene glycol, butylene glycols, diethyleneglycol and triethylene glycol.

The advantages of producing dimethylaminomethylenebis(phosphonic acid)by the process of this invention are:

1. Very high yields based on the amount of phosphorous trichloride usedare obtained.

2. The toxic and polluting hydrogen chloride is reduced.

3. Valuable chloroalkanes and dichloroalkanes are simultaneouslyproduced with the dimethylaminomethylenebis(phosphonic acid).

4. A wide variety of alcohols and glycols are suitable in the process.

5. Pasty or solid intermediates are elininated which makes the processuseful at commercial scale.

The examples of this invention describe several experiments in whichdimethylaminomethylenebis(phosphonic acid) was prepared in good yieldusing several different glycols and alcohols.

The dimethylaminomethylenebis(phosphonic acid) is usually isolated as anaqueous solution, but it can also be obtained as a crystalline solid.Aqueous solutions of the phosphonic acid or salts of the phosphonic acidcan be mixed with solutions of the polymers in water to prepare thecomposition of this invention. Phosphorous acid, alkali metalphosphites, and water-soluble zinc salts may then be added to theaqueous solutions in varying amounts to prepare the additionalcompositions described in this invention. When zinc salts are used inthe compositions of this invention, it is necessary to decrease the pHof the preparation by addition of the appropriate level of phosphorousacid or another mineral acid to prevent separation of complex zincsalts.

The use of dimethylaminomethylenebis(phosphonic acid) and its alkalimetal and ammonium salts for the inhibition of precipitation ofinsoluble salts from aqueous solutions has been described in U.S. Pat.No. 3,957,160, May 18, 1976. This invention claims that the compound iseffective at a molar ratio of 5×10⁻⁴ to 5×10⁻² mols per mol ofprecipitable salt cation. For dimethylaminomethylenebis(phosphonic acid)these values correspond to ratios of 0.27 to 27 parts of the phosphonicacid per 100 parts of calcium.

Polyacrylic acid, other carboxylic acid polymers and salts of thepolymers are also known to be effective in preventing the precipitationof alkaline earth metal salts and iron salts from aqueous solution.

Neither the dimethylaminomethylenebis(phosphonic acid) nor the polymericcarboxylic acids are completely satisfactory as water treatmentchemicals. The phosphonic acid is most effective in preventing theprecipitation of calcium carbonate, but it is much less effective withregard to precipitation of calcium sulfate, calcium acid phosphate,barium sulfate, and ferric hydroxide. The polymeric carboxylic acids arenot effective as corrosion inhibitors and the literature does not haveany statements concerning corrosion inhibiting properties of thedimethylaminomethylenebis(phosphonic acid).

We have found that the compositions of this invention can bemanufactured efficiently and that these compositions will provideeffective corrosion inhibition of metal parts in contact with aqueoussystems. Surprisingly, these compositions are more effective inpreventing the precipitation of metal salts from aqueous solutions thanwould be expected from the combinations of the individual productsincluded in the compositions. This synergism is particularly noted whenthe compositions are used for scale control at threshold treatmentlevels.

In order to demonstrate the scale inhibiting properties of thecompositions of this invention, we have used anti-precipitation testswith super-saturated solutions of calcium carbonate, calcium sulfate,calcium acid phosphate, barium sulfate, and ferric hydroxide. The mostconvenient test methods are related to the demonstration of a "thresholdeffect," which is defined as a stabilization of super-saturatedsolutions of scale forming salts by less than stoichiometricconcentrations of the anti-precipitants. The mechanism of this effectcurrently postulates that the anti-precipitant is adsorbed on the growthsite of the scalent crystallite during the process of crystallization.This adsorption alters the growth pattern so that the resultant scalentcrystals are formed more slowly and are highly distorted. The retardanceof crystal growth rate lowers the amount of solid scalent deposited onsurfaces. In addition, the distortion of the crystal structure usuallygives the scalent solid a different adherence characteristic and thesurfaces then have a decreased amount of scale accumulation.

This invention is further illustrated by the following specific butnon-limiting examples.

EXAMPLE 1

A reaction flask was charged with 200 grams of bis(2-chloroethyl) etherand 36.5 grams of dimethylformamide and the mixture was treated with 110grams of phosphorous trichloride added dropwise at such a rate that thereaction temperature was maintained between 20° and 45° C. After onehour agitation at this temperature, the reaction was treated with 63.6grams of diethylene glycol which was added at such a rate that thereaction temperature did not exceed 45° C. Agitation was continued fortwo hours at 30° to 45° C. after the addition was complete. The reactionwas warmed slowly to 70° C. and maintained at this temperature forsixteen hours. Twenty grams of water were then added slowly while thetemperature was allowed to increase to 95° to 100° C. The mixture wasagitated for thirty minutes, after which, an additional charge of 100grams of water was made. Once again, the reaction was maintained at 95°to 100° C. for thirty minutes before being cooled to 60° C. andseparated in a separatory funnel. The lower aqueous layer was steamdistilled to remove bis(2-chloroethyl)ether and treated with acetone toprecipitate 72.1 grams (76 percent yield) ofdimethylaminomethylenebis(phosphonic acid)monohydrate. Thebis(2-chloroethyl)ether removed by steam distillation was combined withthe organic layer and a total yield of 283.2 grams (97 percent) wasobtained.

EXAMPLE 2

A reaction flask was charged with 1200 grams of bis(2-chloroethyl) etherand 220 grams of dimethylformamide and the mixture was treated with 660grams of phosphorous trichloride added at such a rate that the reactiontemperature was maintained between 20° and 45° C. After one hour ofagitation at this temperature, the flask was charged with 490 grams ofdiethylene glycol which was added at such a rate that the temperaturedid not exceed 45° C. The flask contents were agitated at 20° to 25° C.for sixteen hours and then transferred to a glass-lined, steelautoclave. The autoclave was heated at 155° to 165° C. for twelve hoursand a pressure of 50 pounds per square inch was observed. After coolingand venting, the autoclave contents were treated with 180 grams of waterand the temperature was allowed to rise to 90° to 95° C. Agitation atthis temperature was continued for thirty minutes and then 1500 grams ofadditional water were added. The reaction mixture was agitated for eighthours and then separated in a separatory funnel. Analysis of the aqueouslayer indicated that a yield of 494.6 grams (94.1 percent) ofdimethylaminomethylenebis(phosphonic acid) had been obtained. The yieldof bis(2-chloroethyl)ether in excess of that added in the beginning ofthe reaction was 553.6 grams (83.8 percent).

EXAMPLE 3

The procedure of Example 1 was followed except that thedimethylaminomethylenebis(phosphonic acid) in the aqueous solution wasdetermined by titration. A yield of 89.3 percent was obtained. The yieldof the bis(2-chloroethyl)ether in excess of that used as solvent was92.1 percent.

EXAMPLE 4

The procedure of Example 1 was followed except that ethylene dichloridewas used in place of bis(2-chloroethyl)ether and ethylene glycol (37.2grams) was used in place of diethylene glycol. The yield of ethylenedichloride in excess of that used as solvent was 50.8 percent and theyield of dimethylaminomethylenebis(phosphonic acid) was 87.7 percent.

EXAMPLE 5

The procedure of Example 1 was followed except that ethylene dichloridewas used in place of bis(2-chloroethyl ether and n-butyl alcohol (88.8grams) was used in place of diethylene glycol. The yield of n-butylchloride was 39.2 percent and the yield ofdimethylaminomethylenebis(phosphonic acid) was 75.5 percent.

EXAMPLE 6

The procedure of Example 1 was followed except that n-dodecyl chloridewas used in place of bis(2-chloroethyl)ether and n-dodecyl alcohol (224grams) was used in place of diethylene glycol. The yield of dodecylchloride in excess of that used as solvent was 82 percent and the yieldof dimethylaminomethylenebis(phosphonic acid) was 56.9 percent.

EXAMPLE 7

A composition containing 15 percent ofdimethylaminomethylenebis(phosphonic acid) and 15 percent ofpoly(acrylic acid) in water was prepared by mixing 47.5 grams of anaqueous solution containing 31.6 percent of the trisodium salt ofdimethylaminomethylenebis(phosphonic acid), 35.2 grams of an aqueoussolution containing 42.6 percent of poly(acrylic acid)(molecularweight--3000), and 17.3 grams of water.

EXAMPLE 8

The solutions of dimethylaminomethylenebis(phosphonic acid) andpoly(acrylic acid) referred to in Example 7 were used to prepare twoformulations. The first contained 17.0 percent each of the phosphonateand polymer and the second solution contained 20.0 percent of thephosphonate and 13.0 percent of the polymer. Each of these solutions wasthen mixed with an aqueous solution containing 70 percent of phosphorousacid to prepare the following compositions:

    ______________________________________                                                Phosphonate Polymer   Phosphorous acid                                Number  Percent     Percent   Percent                                         ______________________________________                                        8A      16.2        16.2      3.5                                             8B      15.3        15.3      7.0                                             8C      14.4        14.4      10.5                                            8D      19.0        12.4      3.5                                             8E      18.0        11.7      7.0                                             8F      17.0        11.0      10.5                                            ______________________________________                                    

EXAMPLE 9

A composition was prepared using a 31.0 percent solution of thetrisodium salt of dimethylaminomethylenebis(phosphonic acid), a 45.6percent solution of poly(acrylic acid) with a molecular weight of3300-3500, 70 percent phosphorous acid, 50 percent sodium hydroxide andwater to provide the following concentrations:

    ______________________________________                                        Phosphonate           16.5 percent                                            Poly(acrylic acid)    11.0 percent                                            Phosphorous acid       6.0 percent                                            Sodium hydroxide       5.5 percent                                            ______________________________________                                    

The corrosion inhibiting properties of solutions of this compositionwith zinc chloride were determined in Example 11.

EXAMPLE 10

One hundred grams of a solution containing 20 percent of the trisodiumsalt of dimethylaminomethylenebis(phosphonic acid) and 13 percent of3300-3500 molecular weight poly(acrylic acid) were mixed with 15 gramsof 37 percent hydrochloric acid and 40 grams of a 50 percent solution ofzinc chloride. The corrosion inhibiting results using this compositionare included in Example 11.

EXAMPLE 11

This example illustrates the corrosion-inhibiting properties of thecompositions. The test apparatus included a sump, a flow circuit, acirculating pump, and a heater. A test fluid was prepared to approximatea moderately hard well water concentrated 4 times which did not come incontact with any metal except for test coupons placed within the circuitin a manner simulating flow, impingement, and sump conditions. The testcoupons were 1010 mild steel, and the circulating solution had a calciumhardness as CaCO₃ of 270 parts per million, a magnesium hardness asCaCO₃ of 170 parts per million, chlorie as NaCl of 500 parts permillion, and sulfate as Na₂ SO₄ of 624 parts per million.

The temperature during the test was maintained at about 55° C., and thepH varied from 7 to 9. The test fluid was circulated continuouslythrough the system containing the coupons for a period of seven days.The steel coupons were removed and examined for scale. No significantamount of scale was observed on any of the coupons protected by thecompositions of this invention. The coupons were then cleaned andweighed and the corrosion rates calculated as mils per year. One mil peryear loss is equal to a volume decrease of 0.001 inch per year or 0.0254millimeter per year. The corrosion rates are included in Table 1.

                  Table 1                                                         ______________________________________                                        Corrosiion test results using the compositions of                             Examples 7, 8, 9, and 10                                                      Corrosion                  Corrosion rate in                                  inhibiting                                                                             active    Zinc*   mils per year                                      composition                                                                            ingredient                                                                              added          Impinge-                                    Example No                                                                             Parts per million                                                                           Current  ment   Sump                                   ______________________________________                                        7        30        --      48     99     32                                   7        45        --      44     73     38                                   7        60        --      27     55     25                                   7        60        2       15     20     16                                   7        60        4       10     18     9                                    7        60        6       12     15     19                                   8A       36        --      18     26     20                                   8B       38        --      15     18     14                                   8C       40        --      29     38     29                                   8D       35        --      20     33     31                                   8E       37        --      10     15     15                                   8F       38        --      11     17     11                                   9        33.5      3.4     11     23     9                                    9        33.5      6.7     4      3      4                                    9        33.5      10.1    3      3      3                                    9        33.5      13.4    2      3      2                                    10       5.4       1.5     27     112    41                                   10       10.7      3.1     10     6      8                                    10       16.0      4.6     9      24     14                                   10       21.3      6.2     2      2      1                                    10       31.9      9.3     2      2      2                                    Control  --        --      56     186    44                                   ______________________________________                                         *The composition of Example 10 contained zinc in the concentrated             formulations.                                                            

The results of these tests clearly demonstrate that compositions of thisinvention have excellent corrosion inhibiting properties when testedagainst steel coupons in a very aggressive aqueous system.

EXAMPLE 12

The compositions of this example were tested as scale inhibitingpreparations in Examples 13-17.

                                      Table 2                                     __________________________________________________________________________    Trisodium salt of                                                             dimethylamino-                                                                methylenebis(phos-                                                                         Poly(acrylic acid)                                                                        Phosphoric                                                                           Phosphorous                                   phonic acid) Mol Wt = 3000-5000                                                                        acid   acid                                          Percent      Percent     Percent                                                                              Percent                                       __________________________________________________________________________    (Based on total of active materials)                                          A 100        --          --     --                                            B --         100         --     --                                            C 75         25          --     --                                            D 50         50          --     --                                            E 25         75          --     --                                            F 61         39          --     --                                            G 48         32          20     --                                            H 43         28          29     --                                            I 54         36          --     10                                            J 49         32          --     19                                            K 72         28          --     --                                            L 81         19          --     --                                            M 50         32          --     18                                            __________________________________________________________________________

EXAMPLE 13

Compositions of this invention included in Table 2 were compared forinhibition of calcium carbonate with the trisodium salt ofdimethylaminomethylenebis(phosphonic acid) and poly(acrylic acid). Thetest was conducted by adding to a bottle 100 milliliters of 0.04 percentsolution of calcium hydroxide freshly prepared from recently boileddemineralized water. The compositions being tested were added to providethe calculated concentration desired. Then, 100 milliliters of a 0.05percent solution of sodium bicarbonate prepared from recently boileddemineralized water was added to the bottle. The final volume wasadjusted to 220 milliliters and the solutions were allowed to stand for18 hours at room temperature. The contents of the bottles were filteredthrough Whatman No. 4 filter paper, and the filtered solutions wereanalyzed for calcium content using an atomic absorption instrument or anEDTA titration procedure. The concentration was 98 parts per millioncalcium which is equivalent to 245 parts per million of calciumcarbonate. The percentage inhibition of precipitation was calculated bydividing the calcium content of the filtrate by 98 and multiplying by100. The results obtained are included in Table 3.

The results of these tests show thatdimethylaminomethylenebis(phosphonic acid)(A) and poly(acrylic acid)(B)will inhibit the precipitation of calcium carbonate. When the two arecombined in various proportions (C, D, E, F), the antiprecipitantproperties are maintained and the results with F actually indicate thatthe overall effectiveness is better than that expected from thecombination (synergism). When the phosphonate and poly(acrylic acid) arecombined with phosphoric acid (G and H), the antiprecipitant property isgreatly decreased. However, combinations with phosphorous acid (I and J)maintain the high level of antiprecipitant effect and the corrosioninhibiting property of the composition containing phosphorous acid wasdemonstrated in Example 11. The startling difference observed withcompositions containing phosphoric and phosphorous acids is completelyunexpected because of the similarity of the two acids and the relativelack of information in the literature concerning the use of phosphorousacid in water treatment chemical compositions.

                  Table 3                                                         ______________________________________                                        Results of antiprecipitation tests with calcium carbonate                               Composition                                                         Concentration                                                                             A     B      C   D   E   F   G   H   I   J                        Parts per million                                                                         Percent inhibition                                                ______________________________________                                        1           16    7      10  16  16  18  --  --  14  13                       2           31    25     28  39  36  35  33  27  27  30                       3           43    19     48  73  61  55  --  --  43  45                       4           67    99     80  84  74  78  47  35  55  61                       5           83    100    88  89  82  95  --  --  70  79                       6           98    97     85  85  82  98  53  40  90  92                       7           94    95     85  85  85  99  --  --  92  97                       8           99    97     85  83  88  96  54  42  92  97                       ______________________________________                                    

EXAMPLE 13

The compositions included in Table 2 were tested for inhibition ofcalcium sulfate scale. This test was conducted by mixing in a bottle 10milliliters of a solution containing 162.9 grams of calcium chloride perliter of solution (prepared with deionized water) and the desired volumeof inhibitor stock solution to provide the desired concentration in afinal total volume of 175 milliliters. The pH was then adjusted withdilute HCl or dilute NaOH solutions to 7.0. Twenty-five milliliters ofNa₂ SO₄ solution containing 83.45 grams of Na₂ SO₄ per liter of solutionwas added to the bottle. The final volume was adjusted to 175milliliters if necessary and the bottle was shaken on a gyratory shakertable at room temperature for 18 hours. Each bottle contained 10,000parts per million of calcium sulfate.

After shaking, the contents of the bottles were filtered through WhatmanNo. 4 filter paper and the filtrates were analyzed for calcium contentusing an atomic absorption spectrophotometer or an EDTA titrationprocedure. It was necessary to dilute the filtrate before analysis ifthe calcium content was high. The percentage inhibition of precipitationwas calculated by dividing the calcium content of the filtrate by 2940and multiplying by 100. The results are included in Table 4.

The results included in Table 4 show that the trisodium salt ofdimethylaminomethylenebis(phosphonic acid)(A) is not an effectivecontrol agent for calcium sulfate. Although poly(acrylic acid) wasconsistent, it did not inhibit precipitation of calcium sulfate by asmuch as 70 percent as 10 parts per million. When various combinations ofthe phosphonic acid and polymer were used (C, D, E, F, K, L), excellentinhibition was obtained in every case. For example, composition D gave97 percent inhibition of the calcium sulfate at one part per million.All of the combinations were much more effective than would have beenexpected from the test results with either component, and there is nodoubt that synergism was demonstrated in these tests.

                  Table 4                                                         ______________________________________                                        Results of antiprecipitation tests with calcium sulfate                                 Composition                                                          Concentration                                                                            A      B      C   D   E   F    K    L                             Parts per million                                                                         Percent inhibition                                                ______________________________________                                        1           --     62     --  97  --  --   --   --                            2           --     59     --  97  --  --   --   --                            3           --     59     97  86  62   93   79   72                           4           --     69     97  90  55   90   86   72                           5           7      69     86  97  62   90   97   83                           6           10     66     86  90  79  100  100  100                           7           7      55     90  97  76  100  100  100                           8           0      66     83  94  90  100  100  100                           9           14     66     93  94  89  100  100  100                           10          3      62     79  97  90  100  100  100                           ______________________________________                                    

EXAMPLE 15

The compositions included in Table 2 were tested for inhibition ofbarium sulfate scale. The same procedure as that described in Example 13was used except that the concentration of barium sulfate present was 255parts per million. The barium solution used contained 5.35 grams ofBaCl₂.2H₂ O per liter of solution and the sulfate solution contained1.24 grams of Na₂ SO₄ per liter of solution. After filtration, thesolutions were analyzed for barium using atomic absorptionspectrophotometry. The results of the tests are included in Table 5.

The results from the table show that the trisodium salt ofdimethylaminomethylenebis(phosphonic acid)(A) is not a good inhibitorfor barium sulfate precipitation but that poly(acrylic acid) is a goodinhibitor. Combinations of the two materials (C, D, E, F) showintermediate effectiveness. However, the outstanding feature of Table 5is related to the excellent and unexpected results obtained whenphosphorous acid is added to the combination of the phosphonic acid andpoly(acrylic acid)(M). Composition M gave 75 percent inhibition at aconcentration as low as 3 parts per million and 100 percent at 6 partsper million.

                  Table 5                                                         ______________________________________                                        Results of antiprecipitation tests with barium sulfate                                  Composition                                                          Concentration                                                                            A      B      C    D    E    F    M                               Parts per million                                                                         Percent inhibition                                                ______________________________________                                         3          7      17      7    0    7    7    75                              6          7      37     12   33   27   25   100                              9          7      43     23   30   47   52   100                             12          7      70     23   33   57   71   100                             15          7      94     77   67   87   80   100                             18          3      96     37   33   83   91   100                             21          3      100    40   50   77   91   100                             24          3      90     57   63   67   88   100                             27          0      96     57   67   90   87   100                             30          3      96     63   73   87   100  100                             ______________________________________                                    

Solution M contained 50 percent of trisodiumdimethylaminomethylenebisphosphonate, 32 percent of poly(acrylic acid)and 18 percent of phosphorous acid on a 100 percent active basis asdescribed in Table 2.

EXAMPLE 16

The compositions included in Table 2 were tested for inhibition ofcalcium acid phosphate precipitation. The same procedure as thatdescribed in Example 13 was used except that the concentration ofcalcium acid phosphate (CaHPO₄) present was 300 parts per million. Thecalcium solution contained 4.89 grams of CaCl₂ per liter of solution andthe phosphate solution contained 4.70 grams of Na₂ HPO₄.7H₂ O per literof solution. The filtered solutions were analyzed by an EDTA titrationprocedure. The results of these tests are included in Table 6.

Poly(acrylic acid)(B) is a good inhibitor of CaHPO₄ but the trisodiumsalt of dimethylaminomethylenebis(phosphonic acid) is only fair ineffectiveness. Combinations of the two materials (C, D, E) provided goodinhibition of CaHPO₄ at intermediate concentrations and Composition Ewas even more effective than would be expected from combination of thetwo materials.

                  Table 6                                                         ______________________________________                                        Results of antiprecipitation tests with calcium acid phosphate                          Composition                                                          Concentration                                                                            A       B       C     D      E                                    Parts per million                                                                         Percent inhibition                                                ______________________________________                                         3           0       17      0    0       0                                    6           0       13      0    0       0                                    9          73       37     57    17      30                                  12          73      100     60    80     100                                  15          63      100     100   77     100                                  18          67      100     87    77     100                                  21          63      100     87    83     100                                  24          70      100     90    100    100                                  27          60      100     83    100    100                                  30          70      100     87    100    100                                  ______________________________________                                    

EXAMPLE 17

Inhibition of ferric hydroxide precipitation by compositions included inTable 2 was evaluated. A solution containing 14.5 grams of ferricchloride (FeCl₃) per liter of solution was diluted 1 to 50 withdeionized water. One hundred milliliters of the dilute solution weremixed with stock solutions of compositions A, B, and D. The volume wasmade to 200 milliliters, and the pH was adjusted to 9.0 with sodiumhydroxide solution. The bottles were allowed to stand for 24 hours andwere observed for presence of a brown-orange precipitate of ferrichydroxide. Concentrations of 20 parts per million of A and B wererequired to inhibit precipitation but only 15 parts per million ofcomposition D were required to inhibit precipitation of the ferrichydroxide.

EXAMPLE 18

A composition similar to Composition D in Table 2 was prepared by mixinga solution of dimethylaminomethylenebis(phosphonic acid) and a solutionof a polymer prepared by polymerizing acrylonitrile and hydrolyzing thepolymer with sodium hydroxide to a mixture of sodium polyacrylate andpolyacrylamide. The solution was formulated so that approximately equalamounts of the phosphonic acid and polymer were present. Thiscomposition was effective as an antiprecipitant and as a corrosioninhibitor.

EXAMPLE 19

A composition similar to Composition D in Table 2 was prepared by mixinga solution of dimethylaminomethylenebis(phosphonic acid) and a solutionof a polymer prepared by polymerizing maleic anhydride and subsequentlyhydrolyzing the anhydride group to carboxylic acid groups with sodiumhydroxide. The molecular weight of the polymer was in the range of 800to 2000. The solution was formulated so that approximately equal amountsof the phosphonic acid and polymer were present. This composition waseffective as an antiprecipitant and as a corrosion inhibitor.

EXAMPLE 20

A composition was prepared from an aqueous solution of the trisodiumsalt of dimethylaminomethylenebis(phosphonic acid), an aqueous solutionof poly(acrylic acid) having a molecular weight of 4000, an aqueoussolution containing 70 percent phosphorous acid, an aqueous solutioncontaining 50 percent sodium hydroxide, and water. The concentrationpresent was 17 percent of the trisodium salt ofdimethylaminomethylenebis(phosphonic acid), 11 percent of poly(acrylicacid), 6 percent of phosphorous acid, and 5.5 percent of sodiumhydroxide. This composition was effective as an antiprecipitant and as acorrosion inhibitor.

EXAMPLE 21

A corrosion and scale inhibiting composition was prepared by mixing 100grams of an aqueous solution containing 20 percent of the trisodium saltof dimethylaminomethylenebis(phosphonic acid) and 13 percent ofpoly(acrylic acid) having a molecular weight of 3200, 15 grams of 35percent hydrochloric acid, and 50 grams of an aqueous solutioncontaining 50 percent of zinc chloride.

EXAMPLE 22

A corrosion and scale inhibiting composition was prepared by mixing 100grams of an aqueous solution containing 18 percent of the trisodium saltof dimethylaminomethylenebis(phosphonic acid), 11.7 percent ofpoly(acrylic acid) having a molecular weight of 3200, and 7 percent ofphosphorous acid, 25 grams of 37 percent hydrochloric acid solution, and50 grams of an aqueous solution containing 50 percent of zinc chloride.

While particular embodiments of the invention have been described, itwill be understood, of course, that the invention is not limited theretosince many modifications may be made; and it is, therefore, contemplatedto cover by the appended claims any such modifications as fall withinthe spirit and scope of the invention.

The invention having thus been described, what is claimed and desired tobe secured by Letters Patent is:
 1. A corrosion and scale inhibitingcomposition consisting essentially of on a weight basis: about 10 toabout 90% dimethylaminoethylenebis-(phosphonic acid) or a water-solublesalt thereof, a water-soluble polymer having a linear hydrocarbonstructure with side chain carboxylic groups exemplified by thestructure: ##STR4## wherein R is hydrogen or --COOH and R' is hydrogenor methyl in an amount varying from about 10 to about 90% and one ormore of the following:A. water B. about 0 to 25% of an aqueous solutionof phosphorous acid or an alkali metal salt thereof, or C. about 1.5 toabout 13.5% of an aqueous solution of a water soluble zinc salt.
 2. Thecomposition of claim 1 wherein the water soluble polymer is poly(acrylicacid).
 3. The composition of claim 1 wherein the water soluble polymeris poly(methacrylic acid).
 4. The composition of claim 1 wherein thewater soluble polymer is hydrolyzed poly(maleic anhydride).
 5. Thecomposition of claim 1 wherein the water soluble polymer is hydrolyzedpolyacrylonitrile.
 6. The composition of claim 1 wherein the watersoluble polymer is hydrolyzed polyacrylamide.
 7. The composition ofclaim 1 wherein the dimethylaminomethylenebis (phosphonic acid) andwater soluble polymer are dissolved in water.
 8. The composition ofclaim 1 wherein the dimethylaminomethylenebis (phosphonic acid) andwater soluble polymer are combined with aqueous phosphorous acid.
 9. Thecomposition of claim 1 wherein the dimethylaminomethylenebis (phosphonicacid) and water soluble polymer are combined with aqueous zinc chlorideand hydrochloric acid.
 10. The composition of claim 1 wherein thedimethylaminomethylenebis (phosphonic acid) and water soluble polymerare combined with phosphorous acid, zinc chloride, hydrochloric acid,and water.
 11. A process for inhibiting corrosion and scaling of metalsurfaces in water systems consisting essentially in adding to water insaid systems an effective amount of a composition consisting essentiallyof on a weight basis: about 10 to about 90% dimethylaminomethylenebis(phosphonic acid) or a water-soluble salt thereof, a water-solublepolymer having a linear hydrocarbon structure with side chain carboxylicacid groups exemplified by the structure: ##STR5## wherein R is hydrogenor --COOH and R' is hydrogen or methyl in an amount varying from about10 to about 90% and one or more of the following:A. water B. about 0 to25% of an aqueous solution of phosphorous acid or an alkali metal saltthereof, or C. about 1.5 to about 13.5% of an aqueous solution of awater-soluble zinc salt.
 12. A process for inhibiting corrosion andscaling of metal surfaces in water systems according to claim 11consisting essentially in adding to water in said systems from 0.5 to1000 parts per million parts of water of the composition as defined inclaim
 11. 13. A process for inhibiting corrosion and scaling of metalsurfaces in water systems according to claim 11 consisting essentiallyin adding to water in said systems an effective amount of thecomposition as defined in claim 11 wherein the water soluble polymer ispoly(acrylic acid).
 14. A process for inhibiting corrosion and scalingof metal surfaces in water systems according to claim 11 consistingessentially in adding to water in said systems an effective amount ofthe composition as defined in claim 11 wherein the water soluble polymeris poly(acrylic acid) and the composition phosphorous acid.
 15. Aprocess for inhibiting corrosion and scaling of metal surfaces in watersystems according to claim 11 consisting essentially in adding to waterin said systems an effective amount of the composition as defined inclaim 11 wherein the water soluble polymer is poly(acrylic acid) and thecomposition contains zinc chloride.
 16. A process for inhibitingcorrosion and scaling of metal surfaces in water systems according toclaim 11 consisting essentially in adding to water in said systems aneffective amount of the composition as defined in claim 11 wherein thewater soluble polymer is poly(acrylic acid) and the composition containsphosphorous acid, zinc chloride, and hydrochloric acid.
 17. A processfor inhibiting corrosion and scaling of metal surfaces in water systemsaccording to claim 11 consisting essentially in adding to water in saidsystems from 0.5 to 1000 parts per million of the composition as definedin claim 11 comprising dimethylaminomethylenebis(phosphonic acid),poly(acrylic acid), and water.
 18. A process for inhibiting corrosionand scaling of metal surfaces in water systems according to claim 11consisting essentially in adding to water in said systems from 0.5 to1000 parts per million of the composition as defined in claim 11comprising dimethylaminomethylenebis(phosphonic acid), poly(acrylicacid), phosphorous acid, and water.
 19. A process for inhibitingcorrosion and scaling of metal surfaces in water systems according toclaim 11 consisting essentially in adding to water in said systems from0.5 to 1000 parts per million of the composition as defined in claim 11comprising dimethylaminomethylenebis(phosphonic acid), poly(acrylicacid), zinc chloride, hydrochloric acid, and water.
 20. A process forinhibiting corrosion and scaling of metal surfaces in water systemsaccording to claim 11 consisting essentially in adding to water in saidsystems from 0.5 to 1000 parts per million of the composition as definedin claim 11 comprising dimethylaminomethylenebis(phosphonic acid),poly(acrylic acid), phosphorous acid, zinc chloride, hydrochloric acid,and water.